God changes us over time. That change begins with the lesson–which may take a lifetime to learn in the way that it really needs to be learned–that the first thing we must do is to give up trying to justify, or vindicate, ourselves. Abandoning the desire for self-justification is the necessary precondition for receiving God’s mercy toward and forgiveness of our sins–or rather of our other sins, since the desire for self-justification is itself sin.
Augustine points this out in Confessions 10.58, where he writes:
…aliquid nos reducet in spem nisi nota misericordia tua, quoniam coepisti mutare nos? Et tu scis, quanta ex parte mutaveris, qui me primitus sanas a libidine vindicandi me, ut propitius fias etiam ceteris omnibus iniquitatibus meis et sanes omnes languores meos et redimas de corruptione vitam meam et corones me in miseratione et misericordia et saties in bonis desiderium meum, qui compressisti a timore tuo superbiam meam et mansuefecisti iugo tuo cervicem meam.
But will anything except your known mercy bring us back into hope? You have begun to change us. You know to what a great degree you’ve changed me, at first curing my itch to justify myself, 1 so that you could become forgiving toward all of my other sins as well, healing all my diseases and buying back my life from rotting in the grave, and crowning me with your tender mercy and tenderheartedness, and satisfying my desire with good things, after you suppressed my arrogance with the fear of you, and tamed me to take your yoke on my neck. (tr. Sarah Ruden, emph. hers)
Augustine’s emphasis on God’s mercy alone as the foundation of the believer’s faith echoes what he had said earlier in the book (10.48):
Una spes, una fiducia, una firma promissio misericordia tua.
There is one hope, one faith, and one solid promise: your mercy. (tr. Ruden)